Atherosclerosis and its clinical consequences, coronary heart disease (CHD), stroke and peripheral vascular disease, represent a truly enormous burden to the health care systems of the industrialized world. In the United States alone, approximately 13 million patients have been diagnosed with CHD, and greater than one half million deaths are attributed to CHD each year. Further, this toll is expected to grow over the next quarter century as the average age of the population increases and as an epidemic in obesity and diabetes continues to grow.
Inhibition of cholesterol ester transfer protein (CETP) is a potential new approach to reducing the incidence of atherosclerosis. Statins, which are widely used to help control cholesterol, are effective in reducing LDL-cholesterol (the “bad cholesterol”) in patients, and are relatively less effective in raising HDL-cholesterol (“the good cholesterol”). CETP inhibitors are effective in raising HDL-cholesterol and may also reduce LDL-cholesterol. CETP inhibitors therefore represent a potential new tool for controlling lipids and for treating or reducing CHD and atherosclerosis in the general population, either alone or in combination with a statin. A combination of a CETP inhibitor and a statin may be especially advantageous in controlling lipids by raising HDL-C and reducing LDL-C.
Pfizer's torcetrapib is the only CETP inhibitor that has so far been tested in a large-scale clinical trial. The trial (named ILLUMINATE) was stopped before its scheduled completion date, because the patients being treated with torcetrapib and atorvastatin in combination had a higher incidence of mortality than the control group, which was being treated only with atorvastatin. Data generated after the termination of the ILLUMINATE trial using animal studies and further data analysis suggest that the higher incidence of mortality in the patient group treated with torcetrapib may have been due to off-target effects of the molecule rather than the mechanism of action. Studies of other CETP inhibitors are therefore expected to occur, and new compounds are still being investigated. Studies of two CETP inhibitors, dalcetrapib and anacetrapib, are starting or are in progress.
CETP inhibitors are generally lipophilic, having poor solubility in water and in aqueous bodily fluids. Oral formulations of the poorly soluble CETP inhibitors using conventional tablet formulations have limited aqueous solubility and generally exhibit a “food effect,” whereby the amount of drug that is absorbed varies, depending on whether the patient takes the drug with a meal or in a fasted state. Efforts have been made to develop formulations that have better bioavailability. A potent class of substituted oxazolidinones, imidazolidinones, and other similar 5-membered heterocycles (see WO 2006/014357 and WO 2006/014413) was recently disclosed. As was observed with other CETT' inhibitors, the compounds have poor water solubility. A particularly active compound that is disclosed in these applications is anacetrapib, which is the oxazolidinone compound pictured herein as compound III. Liquid formulations of the oxazolidinone compounds in surfactants (WO2007/067593) and solid formulations of the oxazolidinone compounds in water soluble polymers (WO2007/092642) have been developed that provide improved solubility and bioavailability compared with conventional formulations of the drugs.
This application discloses an alternative approach to improving the oral availability of the drugs. Prodrugs are disclosed which are easy to administer and which are converted to the active drug in vivo. With the prodrugs of the oxazolidinone compounds that are described in this application, the oxazolidinone ring is formed by a cyclization reaction which forms the active drug after administration to a patient. A somewhat analogous approach has been disclosed in which a 5-membered heterocycle is produced as a by-product of a coupling reaction: W. S. Saari et al., J. Med. Chem., 1990, 33, pp. 97-101.